A plasticating apparatus typically receives polymer or thermoplastic resin pellets, granules or powders, from an inlet port, then heats and works the resin to convert it into a melted or molten state. The melt or molten material is delivered under pressure through a restricted outlet or discharge port to make the finished article. It is desirable that the molten material leaving the apparatus be completely melted and homogeneously mixed, resulting in uniform temperature, viscosity, color and composition.
A typical plasticating apparatus includes an elongated cylindrical barrel, which is usually heated at various locations along its length. An axially supported and rotating screw extends longitudinally through the barrel. The screw is responsible for forwarding, melting, pressurizing and homogenizing the material as it passes from the inlet port to the outlet port. The screw has a core with a helical flight thereon and the flight cooperates with the cylindrical inner surface of the barrel to define a helical channel for forward passage of the resin to the outlet port.
The typical plasticating screw has a plurality of sections along its longitudinal axis with each section being designed for a particular function. Ordinarily, there is a feed section, a transition section, a metering section and a mixing section in series.
As disclosed in U.S. Pat. No. 6,498,399 and illustrated in FIG. 1 a plasticating screw 100 has a main channel defined by a helical flight 113 disposed within and cooperating with an inner-wall of a heated barrel (not shown). As illustrated in FIG. 1, the prior art screw 100 has a longitudinal portion with a plurality of staggered rows of noncontinuous advancing grooves 130 arranged in the main channel thereof. The axis of each row of advancing grooves 130 is substantially parallel to the helical axis of the adjacent helical flight 113 of the longitudinal portion to promote flow in the direction indicated by the arrow 140. A noncontinuous helical channel is formed therein traversing in a reverse direction, compared with the direction of the helical flight 113, the channel having a plurality of retracting grooves 137. While the objective of the retracting grooves 137 is to promote mixing of the polymer or thermoplastic resin pellets in the main channel, in some instances mixing is insufficient.
Based on the foregoing, it is the general object of this invention to provide a screw configured for improved mixing of the polymer or thermoplastic resin pellets.